Physics 4.4 (Waves)

Question 1

How do waves transfer energy and what is the difference between longitudinal and transverse waves?

Answer 1

-Waves transfer energy from one place to another without transferring matter
-Longitudinal waves vibrate parallel to their direction of travel and examples are sound waves and P waves
-Transverse waves vibrate perpendicular to their direction of travel and examples are electromagnetic waves

Question 2

What are progressive waves?

Answer 2

-Waves that transfer energy away from a light source

Question 3

What are two ways we can display a wave

Answer 3

-As a snapshot of the wave profile as the disturbance moves outwards with distance against displacement
-The oscillation of an individual particle with time against displacement

Question 4

What is wavelength, period and frequency of a wave?

Answer 4

-Wavelength is the distance between two adjacent identical points on the oscillation, measured in meters
-Period is the amount of time it takes to complete one pattern of oscillation at any point, measured in seconds
-Frequency is the number of oscillations per unit of time, measured in hertz one oscillation per second

Question 5

What is the amplitude of a wave?

Question 6

What is the phase difference of a wave?

Answer 6

-If two waves have the exact same pattern of oscillation they are said to be in phase.
-Phase difference is the shortest difference between two points on diffferent waves that are in phase
-It can be measured in degrees with 180 degrees representing half a wave or in pie with pie being half a wave and 2 pie as in phase.

Question 7

What is the wave equation and the speed of light and sound?

Answer 7

-V=fλ
-Speed of light= 3*10^8 m/s
-Speed of sound= 340m/s

Question 8

What is the equation for the intensity of a wave? and how is amplitude proportional to intensity?

Answer 8

Intensity=power/area
Intensity is proportional to the square of amplitude for a progressive wave

Question 9

What does the distance between the wavefronts represent in a wavefront diagram?

Answer 9

-Wavelength

Question 10

When is a wave refracted and what can be observed?

Answer 10

-When a wave moves from one material to another which has different optical densities
-The wave will change its speed and if the wave doesn’t pass into the object perpendicular to its surface you will notice a change in the direction

Question 11

What is the diffraction of a wave?

Answer 11

-The spreading out of a wave after passing around an obstacle or through a gap, when the gap width is the same size as the wavelength of the wave

Question 12

What is interference?

Answer 12

-When two or more diffracted wave patterns overlap and interfere with each other creating an interference pattern

Question 13

What are the properties of electromagnetic radiation?

Answer 13

-Can all travel through a vacuum
-Have both a magnetic and electrical wave at right angles to each other
-Travel at the speed of light
-Can all be reflected, refracted, and diffracted
-Can all Demonstrate interference
-Can all be polarised

Question 14

What is ionising radiation and what are the different types of ultraviolets?

Answer 14

-Ultraviolet, x-rays and gamma radiation are all ionising radiation this is because they have the photon energy to knock electrons from the shells of atoms.
-Ultraviolet has three types: ultraviolet A (causes tanning), ultraviolet B (causes damage such a sunburn and skin cancer) and ultraviolet C (filtered out by atmosphere) and are all emitted by the sun

Question 15

What is an unpolarised wave, a plane polarised wave and a polarising filter?

Answer 15

-An unpolarised wave can have an electric field in any number of planes
-A plane-polarised wave is a wave that has fields in only one plane
-A polarising filter causes an unpolarised wave to have oscillating waves in only one plane

Question 16

What will happen if you have a source of light and a polarising filter infront of it and then you rotate another polarising filter through 360 degrees?

Answer 16

-As the second filter is rotated from 0-90 degrees the light intensity decreases until it reaches 90 degrees where no light will be able to pass through light intensity then increases back up to 180 degrees
-This is because the second polarising filter is decreasing the amplitude of the wave when it rotates.

Question 17

What is the equation for refractive index?

Answer 17

n= speed of light in vacuum/speed of light in material

Question 17

How do polarising glasses cut out glare?

Answer 17

-Light that has been reflected can be partially polarised, more light in the direction of oscillation than other directions, polarising glasses can cut out this light reducing glare

Question 18

What is total internal refraction?

Answer 18

• When a wave hits the material with an angle of incidence equal to the critical angle it causes the refracted wave have an angle of refraction of 90 and move along the boundary.

Question 19

What happens when a wave hits a material below or above the critical angle?

Answer 19

-Lower than the critical angle refraction will occur but there will also be a weak reflected ray
-If we increase the angle of incidence above the critical angle only reflection will take place

Question 20

What does the principle of superstition state? and what are the conditions?

Answer 20

-When two or more of the same type of wave meet the resultant wave can be found by adding up the displacements of the individual waves
-The waves must maintain a constant phase difference (coherent)

Question 21

What is constructive and destructive interference?

Answer 21

-Constructive when two waves with the same amplitude that are in phase meet the resultant wave will be twice of the individual waves
-Destructive interference when two waves that are antiphase meet they cancel each other out and the resultant wave has an amplitude of zero

Question 22

What is the difference between path difference and phase difference?

Answer 22

-Both refer to the distance between two waves
-Path difference is measured in wavelength and phase difference pie (a quarter of a wave is wavelength over 4 or pie over 2)

Question 23

Does the difference between constructive and destructive patterns increase or decrease with lower frequencies

Answer 23

Increases

Question 24

What was the purpose of Thomas Youngs double slit experiment?

Answer 24

-To work out the wavelength of light

Question 25

How would you increase the brightness and sharpness of maxima in the youngs double slit experiment

Answer 25

-Increase the number of slits the light has to pass through

Question 26

What are nodes and antinodes?

Answer 26

-Nodes are points on a stationary wave where there is no displacement and antinodes are points where the displacement is maximum

Question 27

What is the fundemental mode of frequency?

Answer 27

• When the length of the string is half the wavelength you produce a wave with its lowest possible fundamental frequency, waves with higher frequencies can be produced called harmonics